Filament behaviour and stability in ECM memristive devices studied by electrochemical impedance spectroscopy.

The filament in the electrochemical metallization memories (ECM/CBRAM) [1,2] and valence change memory (VCM/OxRAM) [2,3] devices defines the low resistive state (LRS) and the transition to the high resistive state (HRS). The stability of the filament (formation or dissolution) is inherently dependent on different chemical, physical and mechanical forces, acting predominantly into the direction of its dissolution. In this work, we study the dynamics of the cell resistance and capacity in SiO2-based ECM/CBRAM devices by electrochemical impedance spectroscopy (EIS). The influence of the frequency range and amplitude is reported and the in operando filament dynamics is discussed. The effect of applied DC voltage magnitude and duration of the pulse on the (in)stability and behavior of the filament is also presented. It is demonstrated that even small voltages in the range of 10 mV can be essential for the resistance changes in both directions. Our work is an essential step to understand the cell dynamics at conditions in a state where already a few atoms may be responsible for a transition into the LRS or the HRS.